Purification of retroviral proteins and performance of radioimmunoassays for retroviral proteins. Preparation of viral and cellular nucleic acids, virus specific DNA probes, and performance of restriction endonuclease digestion and separation of viral and cellular DNA fragments. Performance of molecular hybridization and molecular blotting techniques. Preparation of high quality tissue culture medium, large scale virus and cell production, and biological assays for retrovirus infectivity and transformation. Maintenance of high quality rodent facilities and performance of in vivo tests for oncogenic viruses.